The present invention relates to a milling device and a milling tool having such a milling device, and to a method to produce such a milling device.
For metal cutting tools, many cutting tool materials, i.e. the material of the cutting edges of the cutting tools, are known. Cutting tool materials are arranged in separate and distinct groups of materials, such as high speed steel, cemented carbide, ceramics, cubic boron nitride and diamond. These materials are of different chemical compositions, and have different characteristics and properties, especially relating to toughness and hardness, especially at the high temperatures at or near the cutting edge during cutting.
One aim of past and present cutting tool material development is to develop materials with both high toughness and high hardness. However, so far the choice of cutting tool material is always a compromise between toughness and hardness.
Ceramics or ceramic materials are very hard and heat resistant, more so than cemented carbide, and are therefore useful in high cutting speed metal cutting. An important advantage for ceramics is their stability at elevated temperatures. Cubic boron nitride is harder than ceramic, but has the drawback of being more expensive than ceramic. Compared to cemented carbide, ceramics are less tough, which means that they are more brittle or more fragile and have less bending strength. Ceramics may be either alumina-based or silicon-based or silicon nitride-based, or a mix of these. They may be reinforced by “whiskers”. Common types of ceramics include Al2O3, Si3N4 and SiAlON.
In certain metal cutting, or machining, operations, such as milling of deep pockets or cavities in a work piece made from a heat resistant super alloy (HRSA), there is a need for a milling tool or milling device which is long and slender, capable of low wear of the cutting edges at high cutting speed, predictable tool life, and high precision i.e. small geometrical deviations on the machined component. Ideally such milling tool or milling device has low production cost and/or few manufacturing steps.
Known milling tools or milling devices for such machining operations include end mills, exchangeable head milling cutters, and milling cutters with flat-shaped inserts.
End mills are normally monolithic bodies of cylindrical shape, which are clamped in chucks. End mills may be made from various materials, cemented carbide is a common choice. U.S. Pat. No. 8,647,025 discloses an end mill which is made from a monolithic piece of ceramic material.
Exchangeable head milling cutters comprise a front exchangeable head with cutting edges which at its rear is mounted in a tool. One way to mount such an exchangeable head in a tool is through mating threads. Such a device is shown in EP2167263B1, where the exchangeable head is made from a monolithic piece of cemented carbide.